Interesting Interactions

[Tglassy]

Terminal Velocity:  The maximum speed a given object will fall through the atmosphere.  Gravity doesn't make you drop at the same speed.  You're constantly speeding up, until you hit Maximum Velocity.  So Windrunners, who can control gravity, can't really fly faster than Maximum Velocity.  Multiple lashing MIGHT be able to overcome this, but eventually, they'd just ignite the atmosphere and burn themselves up.  Like a a meteor. This is caused by friction with the air.  I know Windrunners can somewhat, somehow, sculpt the air around them, but only so much.  If they did it too much, to go at truly incredible speeds, they'd wind up in a vacuum.  Eventually, the friction with the air around them would get to be too much.

But Ededancers control Friction.  In fact, when they use the Surge of Abrasion, Friction isn't a thing to them.  At all.  They pass through things as if they aren't touching them.  Including air, or water.  

If a Windrunner and an Edgedancer, or one with an Honorblade granting either Gravitation or Abrasion, depending, were to go for a flight together?  Abrasion on both of them, and a lashing to the sky.  

There'd be no wind resistance.  There'd be no Terminal Velocity.  Their speed would just keep increasing 32 ft/second squared.  With enough Stormlight, there's literally no limit to the speed they could fly through atmosphere. Or through water.  

Since Wind Runners can keep air around them, they could fly up to space and, with enough Stormlight, alter the course of an asteroid to hit the planet.  Only, it would go through the atomosphere like it wasn't there, slamming into the ground at insane speeds, as if the planet had no atmosphere.  

With just Abrasion, you could cover an arrow and never worry about Wind Resistance.

Or take a rock, lash it in a particular direction, and cover it in Abrasion.  Instant bullet, which, until it's stormlight ran out, would keep increasing in speed and never arch to the ground.  It wouldn't change direction based on ANY outside forces.  

Take a Firearm, and make it Awesome.  No wear and tear from the bullet leaving the gun, no wind resistance.  The bullet would chew through your body with barely slowing down, because you technically can't touch it.  Unless it hit something harder than itself, like a bone, it would just go straight through.  Lash the bullet, and you have a sniper.

Gravity and Abrasion.  That's an insane combination.  

[StanLemon]

Quite true, though I think your asteroid example would require more Stormlight than would ever be practical. 

Honestly, I'm of the opinion that people don't think about how powerful Abrasion by itself is. I would assume Abrasion could also increase friction as well. Running on air, making the air friction so great as to effectively have force fields. And that's just the beginning. So far there is no confirmation in the books that it can be used that way, but it seems a possibility at least.

[+Oltux72 he/him]

It depends on exactly which friction Abrasion controls. Is it just literal friction of stuff rubbing against each other or is it also the aerodynamic drag of moving air out of your way?

In any case on a planetary surface you'd be limited to orbital velocity plus a small addition you'd get from continously adjusting your vector.

[Frustration]

5 hours ago, Tglassy said:

Terminal Velocity:  The maximum speed a given object will fall through the atmosphere.  Gravity doesn't make you drop at the same speed.  You're constantly speeding up, until you hit Maximum Velocity.  So Windrunners, who can control gravity, can't really fly faster than Maximum Velocity.  Multiple lashing MIGHT be able to overcome this, but eventually, they'd just ignite the atmosphere and burn themselves up.  Like a a meteor. This is caused by friction with the air.  I know Windrunners can somewhat, somehow, sculpt the air around them, but only so much.  If they did it too much, to go at truly incredible speeds, they'd wind up in a vacuum.  Eventually, the friction with the air around them would get to be too much.

They can just create vacuums using Adhesion.

[Guest]

I have a few points about this. First, before I get to the critique, yes, I wholeheartedly agree that eliminating friction with the ability to control gravity could make insane projectile weapons and other applications. Roshar hasn't thought through all of the implications of this. I mean, just think about a catapult or a siege wall that took advantage of no abrasion and control over gravity.

Second, the part where you said: 

Quote

Gravity doesn't make you drop at the same speed.  You're constantly speeding up, until you hit Maximum Velocity.  So Windrunners, who can control gravity, can't really fly faster than Maximum Velocity.  Multiple lashing MIGHT be able to overcome this, but eventually, they'd just ignite the atmosphere and burn themselves up

It's half right. The first two sentences are right but the last two are wrong. Terminal velocity happens when the force due to gravity equals the force due to air resistance. If a Windrunner was flying at one lashing, they would eventually hit terminal velocity. They could then added another lashing and would be doubling the gravity part of their equation while not changing anything else. It would allow them to fly faster because the air resistance they were feeling at that instant cancelled out one lashing but wasn't strong enough to cancel out two. 

Third, when you said:

12 hours ago, Tglassy said:

... but eventually, they'd just ignite the atmosphere and burn themselves up. Like a a meteor. This is caused by friction with the air. 

That's wrong too. The heat an object feels while falling is from compression of the air in front of them. Not from friction. The idea goes like this: when you compress a gas, it heats up (you can test this, by the way, with some super glue, a thermometer and a transparent 2 liter). Meteors fly really fast and aren't very aerodynamic so they compress the gas in front of them. Voila, super heating when flying into air. 

Don't get me wrong, obviously eliminating friction will cause projectiles to fly faster. The interaction between a bullet and the barrel is a great example of this but it won't solve the heating problem. 

[StanLemon]

16 minutes ago, DougTheRug said:

It's half right. The first two sentences are right but the last two are wrong. Terminal velocity happens when the force due to gravity equals the force due to air resistance. If a Windrunner was flying at one lashing, they would eventually hit terminal velocity. They could then added another lashing and would be doubling the gravity part of their equation while not changing anything else. It would allow them to fly faster because the air resistance they were feeling at that instant cancelled out one lashing but wasn't strong enough to cancel out two. 

Correct me if I'm wrong, I may be remembering incorrectly. But isn't air resistance caused by friction making it so that the air can't get out of the way in time? 

Sure there would still be the issue of in front of you needing to deal with the rest of the air but it should be able to easily flow around you

[Guest]

Yes, the issue is that air is front of you but it isn't friction. The classic example of friction is from pushing an object across the floor and can be thought of as a force resulting from two objects touching and one (or both) sliding past the other. Air molecules being stuck in front of an object isn't similar.

Lets put some hard guesses on it. I found this article (https://mae.ufl.edu/~uhk/ASTEROID.pdf) from the University of Florida that suggests the impact speed of an asteroid from the asteroid belt would hit at about 24 miles per second and another (https://personal.ems.psu.edu/~bannon/moledyn.html) from Penn State that suggests the speed of air molecule is around 500 meters per second. That means the asteroid is about 77 times faster. This means we can think about the air as nearly stationary when asteroids first come in the atmosphere. Since the ones in front of the asteroid can't get out of the way, they get compressed by the asteroid (like a piston) which means the air in front of the asteroid heats up. And, since the air can be thought of as nearly stationary, then a very small percentage of the molecules of the air not in the path of the asteroid touch it. Since a small number of molecules not being compressed touch the asteroid, what is causing friction? 

[Quantus he/him]

7 hours ago, StanLemon said:

Correct me if I'm wrong, I may be remembering incorrectly. But isn't air resistance caused by friction making it so that the air can't get out of the way in time? 

Sure there would still be the issue of in front of you needing to deal with the rest of the air but it should be able to easily flow around you

We did the math a while back. Those are the two main factors (Friction drag vs volume displacement) are separate and mostly independent factors in Drag calculations, with their own governing equations.  Removing Friction will help a lot, but the faster you get (literally the closer to the Speed of Sound) the more force it takes to shove the mass of air out of the way (compressing it mostly) and the more that side of the equation takes over.  At more reasonable speeds the Friction element plays a bigger role. 

Edited October 29, 2021 by Quantus
Awful spelling...

[Tglassy]

If that's the case, then why do aerodynamic space shuttles create so much heat upon reentry?  Isn't it friction that causes that, since the Aerodynamics of the shuttle allow the air to move around the shuttle easier, without getting 'trapped'?

[Guest]

@Tglassy The space shuttles don't fly in like planes til the end of the descent. And, if you look at their belly, it's covered in ablative heat armor that protects them from the heat of the compression of the air. The ISS orbits at a speed of 18000 miles per hour (5 miles per second) while a 737 cruises at around 600 miles per hour. So, the shuttle has to slow down to 1/30th of the ISS speed to get to the speed that planes typically fly at. It used a technique called aerobraking to slow down which is basically "flying" like an asteroid until slow enough that the airplane controls could handle the speed. As a side note, per my estimate up there, air travels at around 1200 miles per hour. 18000 miles per hour is fast enough to consider air nearly stationary. 

Edited November 1, 2021 by DougTheRug

[+Oltux72 he/him]

On 31.10.2021 at 3:08 PM, Tglassy said:

If that's the case, then why do aerodynamic space shuttles create so much heat upon reentry?  Isn't it friction that causes that, since the Aerodynamics of the shuttle allow the air to move around the shuttle easier, without getting 'trapped'?

1. Once you go supersonic, every shape will form a shockwave. The object is just too fast to transmit the force to the air in front of it.
2. Reentering space craft want to create this effect. You need to lose the energy from orbital velocity, or the eventual interaction with the ground would be detrimental to the existance of the vessel. You can see that in the shape of the warhead of an ICBM. They are designed to reenter without slowing down, as they will lose structural integrity before touching the ground anyway.
3. The way the Shuttle was flown you deliberately prevented aerodynamic lift until the craft was quite slow. Effectively they stalled.

2 hours ago, DougTheRug said:

@Tglassy The space shuttles don't fly in like planes til the end of the descent. And, if you look at their belly, it's covered in ablative heat armor that protects them from the heat of the compression of the air.

I just cannot let that stand. The shuttles didn't use ablative heat shielding. That would be single use. In last consequence they did use radiative and convective cooling.